1. Field of the Invention
The present invention relates to a metallization process for manufacturing semiconductor devices. More particularly, the invention relates to a method for depositing a niobium nitride film by chemical vapor deposition.
2. Background of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) integrated circuits. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on processing capabilities. The multilevel interconnect features that lie at the heart of this technology require careful processing of high aspect ratio features, such as vias, lines, contacts, and other features. Reliable formation of these features is very important to the VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
As circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, i.e., 0.25 xcexcm or less, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Many traditional deposition processes have difficulty filling sub-micron structures where the aspect ratio exceed 4:1, and particularly where it exceeds 10:1. Therefore, there is a great amount of ongoing effort being directed at the formation of void-free, sub-micron features having high aspect ratios.
Conducting metals such as aluminum and copper are used to fill sub-micron features on substrates during the manufacture of integrated circuits. However, aluminum and copper can diffuse into the structure of adjacent dielectric layers, thereby compromising the integrity of the device. Diffusion, as well as interlayer defects, such as delamination, may be prevented by depositing a liner layer or a barrier layer in a feature before depositing the conducting metal. The liner layer is conventionally composed of a metal that provides good adhesion to the underlying material, such as a titanium liner layer. The barrier layer deposited on the liner layer is often a nitride or silicon nitride of that metal which helps protect the underlying material from interlayer diffusion and chemical reactions with subsequent materials.
With the recent progress in sub-quarter-micron copper interconnect technology, niobium and niobium nitride have become attractive as barrier materials in copper applications. Depending on the application, a diffusion barrier layer may comprise a niobium layer, a niobium nitride layer, a niobium/niobium nitride stack, or in combination with other diffusion barrier materials. Niobium and niobium nitride films have been deposited by both physical vapor deposition (PVD) and to a lesser extent, by chemical vapor deposition (CVD) techniques. However, traditional PVD techniques are not well suited for providing conformal coverage on the wall and floor surfaces of high aspect ratio vias and other features. The ability to deposit conformal niobium nitride films in high aspect ratio features by the decomposition of organometallic precursors has gained interest in recent years for developing metal organic chemical vapor deposition (MOCVD) techniques. In such techniques, an organometallic precursor gas is introduced into the chamber and caused to decompose, allowing the metal portion thereof to deposit a film layer of the metal on the substrate.
Currently, there exists only a few commercially available niobium nitride precursors, and the precursors that are available produce films that have unacceptable levels of contaminants, such as carbon and oxygen, which increase the film""s resistivity, and produce films having less than desirable diffusion resistance, low thermal stability, and other undesirable film characteristics. Additionally, as the nitrogen content increases in conducting metal films, the film becomes increasingly resistive, and in the case of niobium nitride, can result in having a film with unacceptably high levels of resistivity, resulting in less than desirable circuit performance.
U.S. Pat. Nos. 5,139,825 (""825) and 5,178,911 (""911) describe the deposition of transitional metal films from dialkylamido compounds at near atmospheric conditions. However, such films generally have less than desirable coverage of sub-micron features formed on a substrate which can lead to void formation in the substrate features and possible device failure. Additionally, the transitional metal films tend to be deposited material on the surfaces of the chamber, which films may subsequently flake or delaminate and become a particle problem within the chamber. Particle deposition in the chamber can produce layering defects in the deposited films and provide less than desirable interlayer adhesion.
Therefore, there remains a need for a process and apparatus for forming conformal metal nitride liner/barrier layers from organometallic precursors in conducting metal metallization, where the metal nitride liner/barrier layers are substantially free of contaminants and have controllable nitrogen contents and controllable film resistivities.
The present invention generally provides a method of depositing a metal nitride material by the decomposition of an organometallic precursor at sub-atmospheric conditions. The metal nitride material is useful as a barrier layer for a conducting metal in an integrated circuit. In one aspect of the invention an organometallic precursor is introduced into a processing chamber and the metal nitride film is deposited by the thermal or plasma enhanced decomposition of the precursor on a substrate at a pressure of less than about 20 Torr in the presence of a processing gas. The deposited niobium nitride film may then be exposed to a plasma to remove contaminants, reduce the film""s resistivity, and densify the film.
The organometallic precursor has the formula Nb(NRRxe2x80x2)5, the formula (NRRxe2x80x2)3Nbxe2x95x90NRxcex94, and combinations thereof, where Nb is niobium, N is nitrogen, and each R, Rxe2x80x2, and Rxe2x80x3 is an organic functional group selected from the group of alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, and combinations thereof. Preferably, the organic functional groups of R, Rxe2x80x2, and Rxe2x80x3 are selected from the group of methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, cyclopentadienyl, benzyl, phenyl, silylated derivatives thereof, fluorinated derivatives thereof, and combinations thereof. The processing gases include nitrogen, hydrogen, ammonia, argon, helium, and combinations thereof, and the post-deposition plasma comprise a gas selected from the group of hydrogen, nitrogen, ammonia, argon, helium, and combinations thereof.
One aspect of the invention provides a method for metallization of a feature on a substrate comprising depositing a dielectric layer on the substrate, etching an aperture within the dielectric layer, depositing a metal nitride layer within the aperture, and depositing a conductive metal layer on the metal nitride layer. The substrate may be optionally exposed to a reactive clean comprising a plasma of hydrogen, argon, and combinations thereof to remove oxide formations on the substrate prior to deposition of the metal nitride layer. The metal nitride layer is niobium nitride deposited by the thermal or plasma enhanced decomposition of an organometallic precursor having the formula Nb(NRRxe2x80x2)5, the formula (NRRxe2x80x2)3Nbxe2x95x90NRxe2x80x3, or combinations thereof, at a pressure less than about 20 Torr in the presence of a processing gas. To remove contaminants, reduce the resistivity of the layer, and densify the layer, the metal nitride layer may then be exposed to a plasma. The conductive metal is preferably copper and may be deposited by physical vapor deposition, chemical vapor deposition, or electrochemical deposition, such as by electroplating.
Yet another aspect of the invention provides a method of depositing a metal nitride film by delivering a steady flow of the precursor to the chamber. The method comprises delivering a liquid precursor having the formula Nb(NRRxe2x80x2)5, the formula (NRRxe2x80x2)3Nbxe2x95x90NRxe2x80x3, or combinations thereof to a vaporizer, vaporizing the liquid precursor, selectively delivering the vaporized precursor through a bypass line connected to an exhaust system to stabilize the vaporization process, selectively delivering the vaporized precursor to a processing chamber, depositing a metal nitride film on a substrate by decomposing the vaporized precursor in the presence of a processing gas to deposit the metal nitride film, and selectively delivering the vaporized precursor through the bypass line connected to the exhaust system to stabilize the vaporization process when exposing the deposited metal nitride film to a plasma or during a substrate transfer operation.